kexdh.c

   1 /*
   2  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26 RCSID("$OpenBSD: kexdh.c,v 1.13 2002/01/25 22:07:40 markus Exp $");
  27
  28 #include <openssl/crypto.h>
  29 #include <openssl/bn.h>
  30
  31 #include "xmalloc.h"
  32 #include "buffer.h"
  33 #include "bufaux.h"
  34 #include "key.h"
  35 #include "kex.h"
  36 #include "log.h"
  37 #include "packet.h"
  38 #include "dh.h"
  39 #include "ssh2.h"
  40
  41 static u_char *
  42 kex_dh_hash(
  43     char *client_version_string,
  44     char *server_version_string,
  45     char *ckexinit, int ckexinitlen,
  46     char *skexinit, int skexinitlen,
  47     u_char *serverhostkeyblob, int sbloblen,
  48     BIGNUM *client_dh_pub,
  49     BIGNUM *server_dh_pub,
  50     BIGNUM *shared_secret)
  51 {
  52         Buffer b;
  53         static u_char digest[EVP_MAX_MD_SIZE];
  54         EVP_MD *evp_md = EVP_sha1();
  55         EVP_MD_CTX md;
  56
  57         buffer_init(&b);
  58         buffer_put_cstring(&b, client_version_string);
  59         buffer_put_cstring(&b, server_version_string);
  60
  61         /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
  62         buffer_put_int(&b, ckexinitlen+1);
  63         buffer_put_char(&b, SSH2_MSG_KEXINIT);
  64         buffer_append(&b, ckexinit, ckexinitlen);
  65         buffer_put_int(&b, skexinitlen+1);
  66         buffer_put_char(&b, SSH2_MSG_KEXINIT);
  67         buffer_append(&b, skexinit, skexinitlen);
  68
  69         buffer_put_string(&b, serverhostkeyblob, sbloblen);
  70         buffer_put_bignum2(&b, client_dh_pub);
  71         buffer_put_bignum2(&b, server_dh_pub);
  72         buffer_put_bignum2(&b, shared_secret);
  73
  74 #ifdef DEBUG_KEX
  75         buffer_dump(&b);
  76 #endif
  77         EVP_DigestInit(&md, evp_md);
  78         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
  79         EVP_DigestFinal(&md, digest, NULL);
  80
  81         buffer_free(&b);
  82
  83 #ifdef DEBUG_KEX
  84         dump_digest("hash", digest, EVP_MD_size(evp_md));
  85 #endif
  86         return digest;
  87 }
  88
  89 /* client */
  90
  91 static void
  92 kexdh_client(Kex *kex)
  93 {
  94         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  95         DH *dh;
  96         Key *server_host_key;
  97         u_char *server_host_key_blob = NULL, *signature = NULL;
  98         u_char *kbuf, *hash;
  99         u_int klen, kout, slen, sbloblen;
 100
 101         /* generate and send 'e', client DH public key */
 102         dh = dh_new_group1();
 103         dh_gen_key(dh, kex->we_need * 8);
 104         packet_start(SSH2_MSG_KEXDH_INIT);
 105         packet_put_bignum2(dh->pub_key);
 106         packet_send();
 107
 108         debug("sending SSH2_MSG_KEXDH_INIT");
 109 #ifdef DEBUG_KEXDH
 110         DHparams_print_fp(stderr, dh);
 111         fprintf(stderr, "pub= ");
 112         BN_print_fp(stderr, dh->pub_key);
 113         fprintf(stderr, "\n");
 114 #endif
 115
 116         debug("expecting SSH2_MSG_KEXDH_REPLY");
 117         packet_read_expect(SSH2_MSG_KEXDH_REPLY);
 118
 119         /* key, cert */
 120         server_host_key_blob = packet_get_string(&sbloblen);
 121         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 122         if (server_host_key == NULL)
 123                 fatal("cannot decode server_host_key_blob");
 124
 125         if (kex->verify_host_key == NULL)
 126                 fatal("cannot verify server_host_key");
 127         if (kex->verify_host_key(server_host_key) == -1)
 128                 fatal("server_host_key verification failed");
 129
 130         /* DH paramter f, server public DH key */
 131         if ((dh_server_pub = BN_new()) == NULL)
 132                 fatal("dh_server_pub == NULL");
 133         packet_get_bignum2(dh_server_pub);
 134
 135 #ifdef DEBUG_KEXDH
 136         fprintf(stderr, "dh_server_pub= ");
 137         BN_print_fp(stderr, dh_server_pub);
 138         fprintf(stderr, "\n");
 139         debug("bits %d", BN_num_bits(dh_server_pub));
 140 #endif
 141
 142         /* signed H */
 143         signature = packet_get_string(&slen);
 144         packet_check_eom();
 145
 146         if (!dh_pub_is_valid(dh, dh_server_pub))
 147                 packet_disconnect("bad server public DH value");
 148
 149         klen = DH_size(dh);
 150         kbuf = xmalloc(klen);
 151         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 152 #ifdef DEBUG_KEXDH
 153         dump_digest("shared secret", kbuf, kout);
 154 #endif
 155         if ((shared_secret = BN_new()) == NULL)
 156                 fatal("kexdh_client: BN_new failed");
 157         BN_bin2bn(kbuf, kout, shared_secret);
 158         memset(kbuf, 0, klen);
 159         xfree(kbuf);
 160
 161         /* calc and verify H */
 162         hash = kex_dh_hash(
 163             kex->client_version_string,
 164             kex->server_version_string,
 165             buffer_ptr(&kex->my), buffer_len(&kex->my),
 166             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 167             server_host_key_blob, sbloblen,
 168             dh->pub_key,
 169             dh_server_pub,
 170             shared_secret
 171         );
 172         xfree(server_host_key_blob);
 173         BN_clear_free(dh_server_pub);
 174         DH_free(dh);
 175
 176         if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
 177                 fatal("key_verify failed for server_host_key");
 178         key_free(server_host_key);
 179         xfree(signature);
 180
 181         /* save session id */
 182         if (kex->session_id == NULL) {
 183                 kex->session_id_len = 20;
 184                 kex->session_id = xmalloc(kex->session_id_len);
 185                 memcpy(kex->session_id, hash, kex->session_id_len);
 186         }
 187
 188         kex_derive_keys(kex, hash, shared_secret);
 189         BN_clear_free(shared_secret);
 190         kex_finish(kex);
 191 }
 192
 193 /* server */
 194
 195 static void
 196 kexdh_server(Kex *kex)
 197 {
 198         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
 199         DH *dh;
 200         Key *server_host_key;
 201         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
 202         u_int sbloblen, klen, kout;
 203         int slen;
 204
 205         /* generate server DH public key */
 206         dh = dh_new_group1();
 207         dh_gen_key(dh, kex->we_need * 8);
 208
 209         debug("expecting SSH2_MSG_KEXDH_INIT");
 210         packet_read_expect(SSH2_MSG_KEXDH_INIT);
 211
 212         if (kex->load_host_key == NULL)
 213                 fatal("Cannot load hostkey");
 214         server_host_key = kex->load_host_key(kex->hostkey_type);
 215         if (server_host_key == NULL)
 216                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
 217
 218         /* key, cert */
 219         if ((dh_client_pub = BN_new()) == NULL)
 220                 fatal("dh_client_pub == NULL");
 221         packet_get_bignum2(dh_client_pub);
 222
 223 #ifdef DEBUG_KEXDH
 224         fprintf(stderr, "dh_client_pub= ");
 225         BN_print_fp(stderr, dh_client_pub);
 226         fprintf(stderr, "\n");
 227         debug("bits %d", BN_num_bits(dh_client_pub));
 228 #endif
 229
 230 #ifdef DEBUG_KEXDH
 231         DHparams_print_fp(stderr, dh);
 232         fprintf(stderr, "pub= ");
 233         BN_print_fp(stderr, dh->pub_key);
 234         fprintf(stderr, "\n");
 235 #endif
 236         if (!dh_pub_is_valid(dh, dh_client_pub))
 237                 packet_disconnect("bad client public DH value");
 238
 239         klen = DH_size(dh);
 240         kbuf = xmalloc(klen);
 241         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 242 #ifdef DEBUG_KEXDH
 243         dump_digest("shared secret", kbuf, kout);
 244 #endif
 245         if ((shared_secret = BN_new()) == NULL)
 246                 fatal("kexdh_server: BN_new failed");
 247         BN_bin2bn(kbuf, kout, shared_secret);
 248         memset(kbuf, 0, klen);
 249         xfree(kbuf);
 250
 251         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 252
 253         /* calc H */
 254         hash = kex_dh_hash(
 255             kex->client_version_string,
 256             kex->server_version_string,
 257             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 258             buffer_ptr(&kex->my), buffer_len(&kex->my),
 259             server_host_key_blob, sbloblen,
 260             dh_client_pub,
 261             dh->pub_key,
 262             shared_secret
 263         );
 264         BN_clear_free(dh_client_pub);
 265
 266         /* save session id := H */
 267         /* XXX hashlen depends on KEX */
 268         if (kex->session_id == NULL) {
 269                 kex->session_id_len = 20;
 270                 kex->session_id = xmalloc(kex->session_id_len);
 271                 memcpy(kex->session_id, hash, kex->session_id_len);
 272         }
 273
 274         /* sign H */
 275         /* XXX hashlen depends on KEX */
 276         key_sign(server_host_key, &signature, &slen, hash, 20);
 277
 278         /* destroy_sensitive_data(); */
 279
 280         /* send server hostkey, DH pubkey 'f' and singed H */
 281         packet_start(SSH2_MSG_KEXDH_REPLY);
 282         packet_put_string(server_host_key_blob, sbloblen);
 283         packet_put_bignum2(dh->pub_key);        /* f */
 284         packet_put_string(signature, slen);
 285         packet_send();
 286
 287         xfree(signature);
 288         xfree(server_host_key_blob);
 289         /* have keys, free DH */
 290         DH_free(dh);
 291
 292         kex_derive_keys(kex, hash, shared_secret);
 293         BN_clear_free(shared_secret);
 294         kex_finish(kex);
 295 }
 296
 297 void
 298 kexdh(Kex *kex)
 299 {
 300         if (kex->server)
 301                 kexdh_server(kex);
 302         else
 303                 kexdh_client(kex);
 304 }